Photographic materials



Patented Nov. 1 2 1946 UNITED STATES PATENT OFFICE PHOTOGRAPHICMATERIALS No Drawing. Application April 7, 1943, Serial No. 482,195. InGreat Britain April 21, 1942 Claims.

This invention relates to the production of sensitive photographicmaterials such as papers, films and plates.

For certain purposes in photography, sensitive papers, films, plates andsimilar materials are required having two or more silver salt emulsions(in practice usually gelatino-silver-halide emulsions of course) whichrespond in different ways to differently coloured lights, and examplesof such materials are given in British specifications Nos. 540,451,540,464, and. 544,134. In the production of these sensitive materialsthe emulsions are sometimes mixed before application to the support, andare sometimes applied successively in layers to the support, that is tosay successively to the same side of the support, sometimes with otherlayers between the emulsion layers. For example, it is common practicein the production of sensitive films and plates for use in colourphotography to apply successively to the support layers of emulsionssensitive to different regions of the spectrum, for instance threelayers adapted to record the blue, green and red portions of the imagerespectively. In some cases in colour photography two or more emulsionscan be mixed in one layer.

Again, multi-contrast printing papers or the like which are capable ofgiving a result of high or low contrast (or a constant contrast usingnegative of difierent contrast) depending on the colour of the lightused in printing can be produced by applying to a paper or other supporta mixture of two emulsions one of which gives an image of high contrastand can be printed by using light of one colour, and the second of whichgives an image of low contrast and can be printed by light of adifferent colour. Instead of a mixture of the two emulsions, they can beapplied successively to the paper or other support.

The different sensitivity of the emulsions to differently coloured lightcan be controlled by the use of sensitising dyes. Thus if two emulsionsare being used in conjunction, one of them may be prepared free from dyeand hence sensitive to blue light but not to light of longer wavelength,and the other may contain a dye sensitising the emulsion to yellowlight, for instance, in which case the second emulsion will be sensitiveto both yellow and blue light, as it possesses a natural sensitivity toblue. The emulsions will thus be sensitive to different ranges of thespectrum. Alternatively, the two emulsions may contain different dyes,so thateach emulsion is dyesensitised over a different spectral range,and in this case one of the emulsions may for in- 2 stance beinsensitive to light of a colour to which a second emulsion is sensitiveand vice versa. Numerous dyes are known which can be used.

In the production of photographic materials of the above type a seriousdifficulty arises, namely, that there is a tendency for the sensitisingdye in one emulsion to wander (or diffuse) to a neighbouring emulsion inwhich its presence is not desired. If this occurs the initial differencein sensitivity between the emulsions is of course reduced, and it mayeven be practically lost. The tendency for a dye to Wander from anemulsion containing it is very marked where the emulsion is mixed withanother. emulsion, and it is in such cases that the difliculty is mostserious. also liable to be serious if the emulsions are appliedsuccessively to the support with no intervening layers between them, sothat the emulsions are therefore in direct contact.

There are various ways of meeting this diniculty. Thus a dye having initself a relatively low tendency to wander can be used, and examples ofsuch dyes are given in British specifications Nos. 524,552 and 532,098.Furthermore, British specifications Nos. 540,451, 540,464 and 544,134disclose that the tendency for sensitising dyes to wander from emulsionscontaining them can be reduced by dispersing various substances such ascertain resins, resin salts and inorganic substances through theemulsions. Another method of reducing this tendency is for the dye to beincorporated in the emulsion actually during manufacture of theemulsion, in which case the dye appears to be more securely attached tothe grains, although this method has certain disadvantages, for instancethat the emulsion is liable to become less contrasty. There is also lesschance of wandering occurring. if-the quantity of dye used is notgreater than is necessary.

The present invention is concerned with a new method of overcoming thedifficulty referred .to

above.

The precise mechanism by which wandering of the dye occurs when adye-sensitised emulsion is mixed with another emulsion or is coated in aneighbouring layer is somewhat uncertain, but it seems that in somemanner dye molecules which should be attached to the grains of thefirstmentioned emulsion become attached to those of the second emulsion.Possibly the dye molecules actually become transferred from the grainsof the one emulsion to those of the other. It is also possible that whenthe first-mentioned emulsion is dye-sensitised a certain number of thedye It is 3 molecules remain unattached to emulsion grains and thatthese molecules subsequently attach themselves to the grains of thesecond emulsion, so that in effect the dye has wandered from the oneemulsion to the other.

It has now been found that the tendency for a sensitising dye to wanderfrom a dye-sensitised emulsion to one or more neighbouring emulsions(which may be dye-sensitised or not) can be reduced by adding a finelydivided silver halide to the first-mentioned emulsion before bringingthe emulsions into association, that is to say before mixing thefirst-mentioned emulsion with the other emulsion or emulsions, if theemulsions are to be mixed, or coating it, if the emulsions are to be inneighbouring layers. It appears probable that in this event many of thedye molecules which might attach themselves to the grains of theneighbouring emulsions actually attach themselves to the silver halideadded to the first-mentioned emulsion and hence do not have theundesirable effect they would have if they wandered to the emulsionswhere their presence is not desired.'

The invention has the advantage that the added silver halide is removedwhen the photographic product is processed in the normal way and doesnot remain and cause a matt effect for instance. Moreover the speed ofthe dyesensitised emulsion to which the silver halide is added is notmaterially affected. The silver halide added to the dye-sensitisedemulsion can be introduced in the form of a sensitive photographicemulsion, and this is preferably of such a character or added in such aquantity that it has relatively little effect on the photographicproperties of the coated photographic material eventually obtained. Thusit may be a relatively slow emulsion when compared with the otheremulsions concerned, so that it does not become developable to any greatdegree when the coated product is exposed. Preferably it is an emulsionhaving grains of a size similar to those of Lippmann emulsions, thereason presumably being that the silver halide grains in such anemulsion have a larger surface area for a given weight of silver'halidethan is the case with other emulsions and hence for a given weight ofsilver halide there is probably more attraction for any available dyemolecules to become attached to the grains. It is in general preferablefor the silver halide to be the same as that present in thedyesensitised emulsion to which it is added, for instance both can besilver bromide or silver chloride, but this is not essential.

The finer the grain of the added silver halide emulsion, where thesilver halide is added in the form of a, sensitive photographicemulsion, the less the quantity that is usually necessary, and if acertain quantity of a large grain emulsion were required then only aquarter of that quantity might be needed if an ordinarily fine grainemulsion were used, or an eighth or even less if the grains were of thesize of those in Lippmann emulsions (the quantities being calculated interms of the silver halide content). In a typical instance the quantityof the added emulsion might be 10% or less of the dye-sensitisedemulsion to which it is added, interms of the silver halide content.Again, the greater the quantity of the added emulsion that is used, thelower should usually be the threshold speed Thisinany event shouldpreferably not be greater than that of the slowest of theother emulsionsconcerned, and it is advantageously not more 4 than a fifth or even atenth of the threshold speed of the slowest of the other emulsions.

The invention can be carried out simply by adding the silver halideemulsion to the dye sensitised emulsion say fifteen minutes after thedye has been added, and then mixing the product with the other emulsionor emulsions (if a mixed emulsion is to be used) or coating it (if it isto be coated in a neighbouring layer). It also seems desirable to add aquantity of the additional silver halide emulsion to the other emulsionor emulsions to the grains of which it is desirable to reduce wanderingof the dye.

It will of course be appreciated that the silver halide to be added mustnot have been so treated, such as by exposureto light, that it developsto silver when the coated photographic product finally obtained isexposed and developed.

The invention is illustrated by the following examples:

Example I To 800 cc. of a contrasty gelatino-silver-bromide emulsioncontainingthe equivalent of 20 grams of silver nitrate there was added asolution of 0.003 gram of 5 (2 ethyl 1 (2) 'benzox azolylideneethylidene) 3 heptyl 1- phenyl- Example II 1,000 cc. of a contrastygelatino-silver: chloride emulsion containing the equivalent of20-g'rams of silver nitrate was dyed with 0.004 gram of the dye referredto in Example I. After 15 minutes there were added cc. of agelatino-silverchloride emulsion containing 2 grams of: silver chlorideand slower than the emulsion to "which it was added.

The product was then mixed' at 25 C.'with 800 cc. of a softgelatino-silver-chloride emulsion containing the equivalent of 20 gramsofsilver nitrate to which 100 cc. of the second emulsion referred to inthe last paragraph (which was also slower than this soft emulsion) had'also'lbeen added, and the mixture was then coated after 30 minutes.

Example III In Example I, instead-of the two emulsions being mixed afterthe additionof the Ifinei'g'rain emulsion to each of them; they wereapplied to a support in adjacent layers. a I

When it is desired to reduce the tendency for the sensitising dye towander fromoneemulsion layer to a neighboring emulsion layer, theadditional silver halide emulsion, insteadfof being added to thedye-sensitised emulsion, loan if de sired be coated betweenthe emulsionlayers This is of especial value where the additional emulsion hasgrains of a size similar to thoseoflLippmann emulsions, and isapplicable to the production of multi-contrast materials in which thehi'gh and low contrast emulsions are; coated in separate layers, V

then coated after30 On a Where there is employed herein the termneighbouring emulsion this is used to indicate that there are twoemulsions between which there is no water-impermeable layer or coatingor the like.

What I claim is:

1. A process for reducing the tendency of a sensitizing dye to Wanderfrom a dye-sensitized photographic silver halide emulsion (1) to anotherphotographic silver halide emulsion (2) in contact with the emulsion (1)comprising incorporating finely-divided silver halide grains of a sizeand photographic speed substantially no greater than the size andphotographic speed of the silver halide grains of a Lippmann typeemulsion in a fluid dye-sensitized photographic silver halide emulsion(1) containing silver halide grains which are of a size and photographicspeed substantially greater than the size and photographic speed of thesaid finely-divided silver halide grains, and then bringing thesotreated dye-sensitized emulsion (1) into contact with anotherphotographic silver halide emulsion (2) containing silver halide grainswhich are of a size and photographic speed substantially greater thanthe size and photographic speed of the said finely-divided silver halidegrains, while at least one of the emulsions (1) and (2) is fluid.

2. A process for reducing the tendency of a sensitizing dye to wanderfrom a dye-sensitized contrasty photographic silver halide emulsion (l)to another photographic silver halide emulsion (2) which is softer thanthe dye-sensitized emulsion (1) and which is in contact with thedye-sensitized emulsion (1) comprising incorporating finely-dividedsilver halide grains of a size and photographic speed substantially nogreater than the size and photographic speed of the silver halide grainsof a Lippmann type emulsion in a fluid dye-sensitized contrastyphotographic silver halide emulsion (1) containing silver halide grainswhich are of a size and photographic speed substantially greater thanthe size and photographic speed of the said finely-divided silver halidegrains, and then bringing the so-treated dyesensitized emulsion (1) intocontact with another photographic silver halide emulsion (2) containingsilver halide grains which are of a size and photographic speedsubstantially greater than the size and photographic speed of the saidfinely-divided silver halide grains and which is softer than thedye-sensitized emulsion (1) while at least one of the emulsions (1) and(2) is fluid.

3. A process for reducing the tendency of a sensitizing dye to wanderfrom a dye-sensitized contrasty photographic gelatino silver halideemulsion (1) to another photographic gelatino silver halide emulsion (2)which is softer than the dye-sensitized emulsion (l) and which is incontact with the emulsion (1) comprising incorporating a photographicgelatino silver halide emulsion of a Lippmann type in a fluiddyesensitized contrasty photographic gelatino silver halide emulsion (1)containing silver halide grains which are of a size and photographicspeed substantially greater than the size and photographic speed of thesilver halide grains of said Lippmann type emulsion, and then bringingthe so-treated dye-sensitized emulsion (1) into contact with anotherphotographic gelatino silver halide emulsion (2) containing silverhalide grains which are of a size and photographic speed substantiallygreater than the size and photographic speed of the silver halide grainsof said Lippmann type emulsion and which is softer than thedye-sensitized emulsion (1), while at least one of the emulsions (1) and(2) is fluid.

4. A process for reducing the tendency of a sensitized dye to wanderfrom a dye-sensitized contrasty photographic gelatino silver bromideemulsion (1) to another photographic gelatino silver bromide emulsion(2) which is softer than the dye-sensitized emulsion (1) and which is incontact with the emulsion (1) comprising incorporating a photographicgelatino silver bromide emulsion of a Lippmann type in a fluiddyesensitized contrasty photographic gelatino silver bromide emulsion(1) containing silver bromide grains which are of a size andphotographic speed substantially greater than the size and photographicspeed of the silver bromide grains of said Lippmann type emulsion, andthen bringing the so-treated dye-sensitized emulsion (1) into contactwith another photographic gelatino silver bromide emulsion (2)containing silver bromide grains which are of a size and photographicspeed substantially greater than the size and photographic speed of thesilver bromide grains of said Lippmann type emulsion and which is softerthan the dye-sensitized emulsion (1), while at least one of theemulsions (1) and (2) is fluid.

5. A process for reducing the tendency of a sensitizing dye to wanderfrom a dye-sensitized contrasty photographic gelatino silver chlorideemulsion (1) to another photographic gelatino silver chloride emulsion(2) which is softer than the dye-sensitized emulsion (1) and which is incontact with the emulsion (1) comprising incorporating a photographicgelatino silver chloride emulsion of a Lippmann type in a fluid.dyesensitized contrasty photographic gelatino silver chloride emulsion(1) containing, silver chloride grains which are of a size andphotographic speed substantially greater than the size and photographicspeed of the silver chloride grains of said Lippmann type emulsion, andthen bringing the so-treated dye-sensitized emulsion (1) into contactwith another photographic gelatino silver chloride emulsion (2)containing silver chloride grains which are of a size and photographicspeed substantally greater than the size and photographic speed of thesilver chloride grains of said Lippmann type emulsion and which issofter than the dye-sensitized emulsion 1), while at least one of theemulsions (1)) and (2) is fluid.

6. The photographic material obtained by the process defined in claim 1.

'7. The photographic material obtained by the process defined in claim2.

8. The photographic material obtained by the process defined in claim 3.

9. The photographic material obtained by the process defined in claim 4.

10. The photographic material obtained by the process defined in claim5.

EDWARD BOWES KNOTT.

